Crystal structure of bis(acetato-κO)bis(pyridine-2-carboxamide oxime-κ2 N,N′)cadmium ethanol disolvate

In this CdII complex incorporating two monodentate acetate groups and two N,N′-chelating pyridine-2-carboxamide oxime ligands, molecules are assembled into chains along the c axis via N—H⋯O hydrogen bonding. The resulting chains are further assembled by ethanol solvent molecules into a three-dimensional supermolecular structure.


Chemical context
The monoanions of simple of 2-pyridyl oximes, (py)C(R)NOH (R = a non-coordinating group, e.g. H, Me, Ph etc.), are remarkable sources of homo-and heterometallic complexes with novel structures and interesting physical properties (Miyasaka et al., 2003;Stamatatos et al., 2007). A logical extension of such studies is the investigation of the coordination chemistry of analogous organic molecules in which the non-donor R group is replaced by a donor group such as pyridine, cyano etc. (Alcazar et al., 2013;Escuer et al., 2011). When R is an amino group, the resulting ligand is pyridine-2amidoxime, (py)C(NH 2 )NOH, which belongs to the class of amidoximes. The presence of the amine functionality is expected to alter the coordination behaviour of this ligand in comparison with that of the (py)C(R)NOH (R = a non-coordinating group) ligands. The characteristics that differentiate the amino group are its coordination capability, potential for deprotonation, different electronic properties and hydrogenbonding effects.
The present work reports the first use of (py)C(NH 2 )NOH in Cd II coordination chemistry and describes the synthesis and structure of the mononuclear title compound.

Structural commentary
The title complex consists of isolated [Cd(O 2 CMe) 2 {(py)-C(NH 2 )NOH} 2 ] complex molecules and ethanol solvent molecules. The central Cd II atom is located on a twofold rotation axis (Wyckoff site 4e). The Cd II atom is coordinated by two monodentate MeCO 2 À groups and two N,N 0 -chelating (py)C(NH 2 )NOH ligands ( Fig. 1 and Table 1). The (py)C(NH 2 )NOH donor atoms are the N atoms of the neutral oxime and the 2-pyridyl groups. The amino N atom of each ligand remains uncoordinating, albeit participating in an extensive intermolecular hydrogen-bonding network. Each of the two coordinating (py)C(NH 2 )NOH molecules results in the formation of a five-membered chelate ring including a Cd II atom, in which the chelate angle N1-Cd1-N1 [86.7 (2) ] is noteably larger than comparable angles found in [Cd(HCO 2 ) 2 (pya) 2 ] (pya = pyridine-2-aldoxime; Croitor et al., 2013). Table 2 shows the hydrogen-bonding interactions. There are two strong symmetry-related intramolecular hydrogen bonds between the unbound oxime (-O1-H1) group and uncoordinating acetate atom O3. Uncoordinating amino atom N2 acts as a donor for two hydrogen bonds; in one of these, the acceptor is coordinating atom O2 from the acetate group, which leads to the formation of chains running along the c-axis direction (Fig. 2). These chains are further linked into a threedimensional network by hydrogen bonds involving the ethanol solvent molecule (O4), acting as a donor for the uncoordinating carboxylate O atom (O3) and as an acceptor for the remaining amino H atom H2B (Table 2 and Fig. 3).

Figure 2
The hydrogen-bonded chain along the c axis. Dashed lines represent hydrogen bonds and H atoms bonded to C atoms have been omitted for clarity.

Figure 3
The crystal structure projected along the c axis. Dashed lines represent hydrogen bonds and H atoms bonded to C atoms have been omitted for clarity.

Figure 1
The title compound with displacement ellipsoids are drawn at the 30% probability level. [Symmetry code: (i) Àx + 1, y, Àz + 3 2 .] and 10 ml DMF, and the solution left to evaporate slowly to afford colourless block-like crystals after three weeks at room temperature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. H atoms bonded to C atoms were placed in geometrically calculated position and were refined using a riding model, with C-H = 0.93 (aromatic) or 0.96 Å (methyl) and U iso (H) = 1.2U eq (C aromatic ) and 1.5U eq (C methyl ). The N-and O-bound H atoms were located in a difference map and the coordinates were refined with N-H = 0.86 (1) Å and U iso (H) = 1.2U eq (N) or 1.5U eq (O).   (Agilent, 2011); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Olex2 (Dolomanov et al., 2009); software used to prepare material for publication: Olex2 (Dolomanov et al., 2009).

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq